|
Posted by Al Dykes on October 31, 2005, 11:51 am
If you were Registered and logged in, you could reply and use other advanced thread options
>1. Eddie Oct 28, 8:30 pm show options
>
>Newsgroups: comp.dcom.lans.ethernet
>Date: 28 Oct 2005 13:30:35 -0700
>Local: Fri, Oct 28 2005 8:30 pm
>Subject: ethernet point to point wiring
>Reply | Reply to Author | Forward | Print | Individual Message | Show
>original | Report Abuse
>
>> I am looking to replace an old serial RS485 multidrop point to point
>> communications line with ethernet but would like to retain the wiring
>> savings in a point to point layout. On RS485 we can connect 32 devices
>> with series point to point wiring. I have done some research that
>> indicates that if I used a switch at each device I would be limited to
>> a maximum of 7. Is this correct, or are new switches able to exceed
>> that number? If so, how many can I realistically connect in a point to
>> point topology.
>
>Is I understand it the 7 hop limit was imposed along
>with a requirement that each bridge should forward
>each frame within one second (or drop it) as part of the
>STP timing budget.
>
>Today these numbers seem somewhat laughable
>(1Gbps for 1 sec would require a 100M Byte buffer)
>however as far as I know (you should check for yourself
>since I have not read 802.1d for years) the standard
>has never been changed in this respect.
>
>There seems to me no reason not to increase the
>number of bridge hops used if STP is not
>involved.
>
>A couple of things to ponder.
>
>Support - If you tell your support channel that you are
>not compliant with the standard then I strongly suspect
>that they will be reluctant to assist.
>
>Probability of packet loss - If you do not recover from
>lost data then you should carefuly consider the
>increased probability of lost packets.
>
>Maintainability - I do not know what you do at present
>however if you were to use low cost switches that
>cannot report or record errors or problems
>it will be very difficult to troubleshoot network
>failures.
>
You didn't say how many stations you want to wire but if it's a small
number, pull wire and do it right. It won't cost much.
If you are doing it for a large operation then do it right or you'll
spend your days under desks and with unhappy users and then your
successor will rewire the place, correctly.
--
a d y k e s @ p a n i x . c o m
Don't blame me. I voted for Gore.
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML site map